Menthol is well known for its physiological cooling effect on the skin and mucous membranes of the mouth and has been extensively used as a flavouring agent (menthol being a major constituent of oil of peppermint) in foodstuffs, beverages, dentifrices, mouthwashes etc. and as a component in a wide range of toiletries, liniments and lotions for topical application. Menthol is also a well known tobacco additive for producing a `cool` sensation in the mouth when smoking.
It is well established that the `cooling` effect of menthol is a physiological effect due to the direct action of menthol on the nerve endings of the human body responsible for the detection of hot or cold and is not due to latent heat of evaporation. It is believed that the menthol acts as a direct stimulus on the cold receptors at the nerve endings which in turn stimulate the central nervous system.
Although menthol is well established as a physiological coolant its use, in some compositions, is circumscribed by its strong minty odour and its relative volatility.
A few other compounds have been reported in the technical literature as having an odour of flavour similar to menthol and from time to time have been proposed as flavourants or odourants in a variety of topical and ingestible compositions. For example, Japanese Patent Publication No. 39-19627 reports that 3-hydroxymethyl p-menthane (methyl carbinol) has a flavour closely resembling that of 1-menthol and suggests its use as a flavourant in confectionery, chewing gum, and tobacco. In Swiss Pat. No. 484,032 certain saccharide esters of menthol are proposed as additives to tobacco. In French patent specification No. 1,572,332 N,N-dimethyl 2-ethylbutanamide is reported as having a minty odour and refreshing effect, and the minty odour of N,N-diethyl 2,2-dimethylpropanamide is also referred to. A similar effect is reported for N,N-diethyl 2-ethylbutanamide in Berichte 39, 1223, (1906). A minty odour has also been reported for 2,4,6-trimethylheptan-4-ol and 2,4,6-trimethyl hept-2-en-4-ol in Parfums-Cosmetiques-Savons, May 1956, pp. 17-20. The cooling effect of menthol and other related terpene alcohols and their derivatives has also been studied and reported in Koryo, 95, (1970) pp. 39-43. 2,3-p-menthane diol has also been reported as having a sharp cooling taste (Beilstein, Handbuch der Organischen Chemie, 4th Ed. (1923) vol. 6, p.744). Still other substituted p-menthanes having a physiological cooling effect are disclosed in German Offenlegungsschrift Nos. P 22 02 535, P 22 03 947, P 22 03 273 and P 22 05 255.
Despite this knowledge of other compounds having an odour and flavour similar to that of menthol, menthol is still extensively used in topicol, ingestible and other compositions notwithstanding the disadvantages mentioned above, namely its very strong odour and its relative volatility, and despite its high cost.